Abstract
Single crystals of 6-chlorouracil containing traces of copper were gamma-irradiated at room temperature and studied using EPR spectroscopy. The ionizing radiation induced the conversion of copper impurities, initially present in the host lattice as Copper(I) complexes, into paramagnetic copper(II) complexes. These complexes exhibited intricate EPR spectra characteristic of Copper(II) complex with two ligated nitrogen atoms. Using EPR spectroscopy, the binding site of Cu(II) ions in a single crystal of 6-chlorouracil was determined. It was proposed that planar coordination bonding to the cupric Cu(II) ion, having two pairs of oxygen and nitrogen atoms as ligands, served to bridge neighboring 6-chlorouracil molecules, thereby replacing a pair of hydrogen bonds with stronger Cu-coordination bonding. The spectroscopic parameters, including g tensor, A(63Cu), and A(14N) tensors, closely resemble those previously reported for copper(II) planar centers in similar systems. However, a small deviation in the principal axes of the g and A(63Cu) tensors from axial symmetry suggests a subtle distortion from the ideal planar geometry of the complex. The theoretically derived spectroscopic parameters further corroborate the proposed structure of the complex.
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